Add comprehensive GitHub Copilot instructions for awsctx development

.github/copilot-instructions.md

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+# awsctx - AWS CLI Context Switcher
+
+awsctx is a powerful bash script for AWS CLI context switching with comprehensive AWS SSO support, profile generation, and advanced features like EKS integration and region heatmaps.
+
+**ALWAYS reference these instructions first and fallback to search or bash commands only when you encounter unexpected information that does not match the info here.**
+
+## Working Effectively
+
+### Prerequisites Installation
+Install all required dependencies before using awsctx:
+- `sudo apt-get update && sudo apt-get install -y curl unzip jq fzf bat`
+- Install AWS CLI v2:
+  ```bash
+  curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip"
+  unzip awscliv2.zip
+  sudo ./aws/install
+  ```
+- Verify prerequisites: `aws --version && jq --version && fzf --version && batcat --version`
+- Required versions: AWS CLI v2, jq 1.6+, fzf 0.40+, bash 4.0+
+
+### Script Setup
+- Make executable: `chmod +x awsctx`
+- **CRITICAL: Always set TERM=xterm** when running: `export TERM=xterm && ./awsctx -h`
+- **NEVER run without TERM set** - script will fail with "unbound variable" errors
+- Script loads in under 1 second for all operations
+- Test basic functionality: `export TERM=xterm && ./awsctx -h`
+
+### Linting and Validation
+- **ALWAYS run shellcheck**: `shellcheck awsctx` -- completes in ~1 second. NEVER CANCEL.
+- The script passes shellcheck with no issues when working correctly
+- No build process required - it's a standalone bash script
+- Dependency check built-in: script will exit with clear error if tools missing
+
+## Key Commands and Timing
+
+All commands complete quickly (under 5 seconds) except when they need to interact with AWS services:
+
+### Help and Information
+- `./awsctx -h` -- Display help (< 1 second)
+- `./awsctx -c` -- Check for updates (may fail without internet access)
+- `./awsctx -v` -- Enable verbose mode
+
+### AWS Configuration (Requires AWS Credentials)
+- `./awsctx -i` -- Initialize AWS SSO configuration (interactive, requires user input)
+- `./awsctx -g` -- Generate AWS config profiles from SSO (timing depends on AWS API)
+- `./awsctx` -- Interactive profile switching (requires existing profiles)
+
+### Advanced Features (Requires Configured AWS)
+- `./awsctx -k` -- Detect EKS clusters and update kubeconfig
+- `./awsctx -m` -- Generate AWS Region Heatmap
+- `./awsctx -r` -- Change region for current context
+- `./awsctx -o json` -- Set output format
+
+## Validation Scenarios
+
+### Basic Functionality Test
+**ALWAYS test these commands after making any changes to ensure the script is working:**
+```bash
+export TERM=xterm  # CRITICAL - script fails without this
+./awsctx -h        # Should display help without errors in < 1 second
+shellcheck awsctx  # Should pass with no issues in < 1 second
+```
+
+**Expected behaviors:**
+- Without `TERM=xterm`: Script fails with "unbound variable" errors
+- Missing dependencies: Script exits with clear error messages like "The 'jq' command could not be found"
+- All help operations complete in under 1 second
+
+### Configuration File Test
+The script creates configuration at `~/.config/awsctx/awsctxrc` or `~/.awsctxrc`. Example valid config:
+```bash
+SSO_START_URL="https://example.awsapps.com/start"
+SSO_REGION="us-east-1"
+SSO_REGISTRATION_SCOPES="sso:account:access"
+CROSS_ACCOUNT_PROFILE="false"
+OUTPUT_FORMAT="json"
+CLI_PAGER=""
+```
+
+### Full User Workflow Test (Requires AWS Access)
+**Note: These commands require valid AWS SSO credentials and cannot be fully tested in environments without AWS access.**
+
+1. Initialize: `./awsctx -i` (interactive setup)
+2. Generate profiles: `./awsctx -g` 
+3. Switch contexts: `./awsctx`
+4. Test EKS detection: `./awsctx -k` (requires kubectl)
+5. Generate heatmap: `./awsctx -m`
+
+### Error Conditions to Test
+**CRITICAL:** Test these scenarios to validate error handling:
+- Running without TERM: `unset TERM && ./awsctx -h` (should show "unbound variable" error)
+- Running without config file: Delete config and run `./awsctx` (should prompt for creation)
+- Running without AWS credentials: `./awsctx` (should show "SSO cache directory not found" and offer to initialize)
+- Missing dependencies: Remove jq/fzf from PATH (should show "command could not be found" with install URL)
+
+## Common Issues and Solutions
+
+### Script Fails with Color/Terminal Issues
+- **Always export TERM=xterm** before running
+- Script requires color terminal support
+
+### Dependency Missing Errors
+- Install missing tools: `sudo apt-get install -y [tool-name]`
+- For bat, use `batcat` command on Ubuntu/Debian systems
+
+### AWS Configuration Issues
+- Script will not work without proper AWS SSO setup
+- Requires internet access for AWS API calls
+- Cannot be fully tested in isolated environments
+
+## Code Structure
+
+### Key Files
+- `/awsctx` - Main executable bash script (48KB)
+- `/README.md` - Documentation and usage instructions
+- No build artifacts or compiled components
+
+### Important Functions
+- `load_config()` - Loads configuration from config file
+- `check_command()` - Validates dependencies
+- `validate_token()` - Checks AWS SSO token validity
+- `generate_config()` - Creates AWS CLI profiles
+- `change_context()` - Interactive profile switching
+
+### Configuration Locations
+- Primary: `~/.config/awsctx/awsctxrc`
+- Fallback: `~/.awsctxrc`
+- AWS config: `~/.aws/config`
+- Kubernetes: `~/.kube/config` (for EKS integration)
+
+## Development Guidelines
+
+### Making Changes
+- **ALWAYS test after every change**: `export TERM=xterm && ./awsctx -h`
+- **ALWAYS run shellcheck**: `shellcheck awsctx` (completes in ~1 second)
+- **NEVER run without TERM set** - causes immediate script failure
+- Ensure script remains executable: `chmod +x awsctx`
+- Test timing expectations: Help should load in < 1 second
+
+### Testing Without AWS
+- Use help command to verify script loads: `./awsctx -h`
+- Test dependency checking by temporarily removing tools
+- Verify configuration file parsing with mock configs
+
+### AWS-Dependent Testing
+- **Cannot be fully automated** without AWS SSO access
+- Test with real AWS environment when possible
+- Mock AWS CLI responses for unit testing if needed
+
+### Performance Expectations
+- Script startup: < 1 second
+- Help display: < 1 second  
+- Shellcheck validation: 1-2 seconds
+- AWS operations: Variable (depends on AWS API response times)
+- Interactive operations: User-dependent
+
+## Repository Context
+
+This is a single-script repository with:
+- No compilation or build process
+- No package.json, Makefile, or similar build files
+- No test suite (manual testing required)
+- Simple Git repository structure
+- Version controlled bash script with documentation
+
+Always validate changes by running the help command and shellcheck before committing any modifications.